Conformational analyses of DNA show that, an addition to sequence specific preferences for mean positions of stacking, there are also substantial sequence specific dependencies in the conformational fluctuations. Both effects manifest themselves in the bending behavior. Consideration of the fluctuations was shown to be especially important for sequences with only small intrinsic static bends. Good agreement was shown between calculations of groove widths for such ensembles of helical forms and the reported hydroxyl radical cutting data. Ways to treat RNA folding in three dimensions were considered. Transfer RNA was used as a test molecule to investigate large numbers of possible arrangements. In the largest generation of such conformations, over 2 million, several types of variant conformations were observed. There was some flexibility in the anticodon loop and several cases of "slip pairing with a single base bulge". Triple helices of several kinds are being investigated. A highly symmetric triple helix structure, with three identical backbones, has been proposed based on fiber X-ray and molecular modelling. Another type of triple helix has been proposed as an intermediate for DNA recombination. It has unusual molecular features such that base triplets are isomorphic, and the helix is sufficiently elongated to weaken interactions between neighboring triplets, thereby circumventing non-specific interactions.